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Blog - Haze vs Mosquitoes

Haze vs Mosquitoes
By Gerald Peck 9/20/2016 10:40 PM

The daytime-active Aedes mosquito is the carrier of multiple fatal diseases, including dengue and the Zika virus.  

Until now, it was believed that seasonal haze dampens dengue activity by being able to kill the Aedes mosquitoes. However, recently, a professor from the the Nanyang Technological University's Lee Kong Chian School of Medicine said otherwise. According to Professor Annelies Wilder-Smith, even if the toxic components of the haze do result in a higher mortality rate of Aedes mosquitoes, the haze may have changed both human and mosquito behaviour in a way that instead of killing the mosquitoes, the haze could instead drive humans and insects closer together when they move indoors to keep away from it.

Singapore is a case in point. In 2013, Singapore was affected by alarming pollution levels. The 24-hour Pollutant Standard Index (PSI) on 22 June 2013 hit the highest reading recorded ever in Singapore, in the ‘very unhealthy’ range of 246. 2013 was also the year when the Health Ministry recorded 22,170 dengue cases in the country –a record.

To reiterate the point, Autoregressive Integrated Moving Average (ARIMA) models were used to investigate the relationship between weekly notifications of dengue and the levels of pollution. The analysis of the model showed no apparent effect of haze on the mosquitoes. 

However, the possibility that haze kills Ades mosquitoes has not been ruled out. According to studies, it may be possible that the toxic components of change both human and vector behaviour in a way that counters the effect of the haze. It was been speculated, as discussed above, that haze drives both mosquitoes and humans indoors. This prolonged stay indoors increases vector to human contact, thereby increasing biting activities and hence dengue infections. In addition to this, since the epidemiology of dengue is very complex and there is an influence of many factors apart from the climate, the role of haze in dengue cannot be excluded with certainty.

Even if it is assumed that haze does have an effect on the survival of the Ades mosquito, it cannot be ignored that in most cases the presence of haze is too short to result in a major effect on the number of dengue cases. The haze that lasted in 2013 was only a week long. We also lack data regarding the extent of effect that haze has on the mosquitoes –is only the biting behaviour affected or is survival affected as well? Thus, the epidemiological evidence present at hand does not lead to a conclusive answer.

In summary, there is no clarity as to whether or not the toxins present in haze have any direct impact on the survival of the Ades mosquito. There is a need for more in-depth study in this area. Several questions remain unanswered.